TEKS 8.10 C
Hot Stuff
TAKS Objective 3 – The student will demonstrate an understanding of the
structures and properties of matter.
Learned Science Concepts:

Matter is composed of atoms.

Substances have chemical and physical properties.

Complex interactions occur between matter and energy.
TEKS Science Concepts 8.10
The student knows that complex interactions occur between matter and energy.
The student is expected to:
(C)
identify and demonstrate that loss or gain of heat energy occurs
during exothermic and endothermic chemical reactions.
Overview
The students will understand that breaking chemical bonds always involves energy.
When bonds are forming energy is released. An endothermic or exothermic reaction is
classified by comparing the amount of energy need to break the chemical bonds of
reactants to the amount of energy released when the bonds of the products are formed. If
less energy is needed to break the bonds of the reactants than to make the products, an
exothermic reaction occurs. The opposite is true when an endothermic reaction occurs.
Though this TEKS focuses on chemical changes, physical properties and physical
changes have been included in the activities. It is important for students to understand
that endothermic and exothermic reactions are also involved in physical changes. Several
activities and assessments compare and differentiate chemical and physical changes.
Instructional Strategies
The activities in this TEKS focus on the concepts of chemical change, exothermic, and
endothermic reactions. Students will make use of their senses to observe a red to yellow
color change as chemicals are combined, cold and hot mixtures, and the production of gas
as evidenced by fizz and bag expansion. Hot/cold packs, making ice cream and various
activities will be used to examine endothermic and exothermic reactions through feel.
Learning Objectives
1. The student will identify endothermic and exothermic reactions associated with
chemical changes.
1. The student will be able to explain how a substance losses or gains heat during a
chemical reaction.
2. The student will identify physical and chemical changes associated with endothermic
and exothermic reactions.
For Teacher’s Eyes Only
This section concentrates on energy changes in chemical and physical processes.
Chemical reactions usually involve the absorption or release of thermal energy. The
energy available from a chemical reaction is chemical potential energy. If a reaction
releases energy, it is called an exothermic reaction; one that takes in heat is called
endothermic.
System and Surroundings
When energy is transferred, it is important to differentiate between what is losing the
energy and what is gaining the energy. By definition, the system is enclosed within the
defined boundaries where we are focusing our attention. Usually, this includes reactants
and products in a chemical reaction, or a single substance in the case of a physical change
like melting or boiling. The surroundings is everything else in the universe which is not
included in the system. When we are looking at a physical change or a chemical reaction,
the surroundings mean the container which holds the reactants and products, any solvent
which is not considered a reactant or product, and the rest of the universe. For example, if
aqueous solutions of hydrochloric acid and sodium hydroxide are mixed, thermal energy
is released by the system – in this case, the reactants. The surroundings – the water, the
container holding the solutions, the air in the room, the rest of the country, etc. absorb the
energy. Any heat lost by the system must be gained by the surroundings, and vice-versa.
Internal Energy
The internal energy of a system is defined by all possible forms of energy in the system.
This includes all the vibrational and rotational motion of molecules and atoms as well as
all the kinetic and potential energy each particle possesses. Since it is impossible to
measure all of this energy, it is impossible to know the total internal energy of a system.
As it turns out, it isn't the absolute internal energy of a system which is important. The
important aspect of a system’s energy is the change in internal energy when a system
changes from one state to another. And this can be determined. There are usually two
types of transformations which dictate a change from state 1 to state 2:
A change in physical state (liquid to gas, solid to liquid, etc.). Energy is absorbed or
released by these processes.
A chemical reaction, in which the reactants represent the initial state and the products
represent the final state. Chemical reactions are accompanied by a gain or loss of energy.
It is important to recognize that internal energy is a state function: its value depends only
on the state of the system, not on how the system arrived at that state. There are two ways
to change the internal energy of a system: add or remove heat, or perform or extract work
from the system.
Hot and Cold Packs
Hot and cold packs demonstrate endothermic and exothermic processes. A cold pack can
be stored at room temperature, but within seconds can become cold enough to ice an
injury. Hot packs meanwhile are often used as hand-warmers in the winter. You can carry
them in your pocket until you are ready to activate them, and they will then stay warm for
15 minutes to half an hour.
A typical cold pack consists of two chambers, one containing water and the other
containing a chemical like ammonium nitrate. When you break the bag, the two chambers
combine and the ammonium nitrate dissolves in the water. This generates a chemical
reaction. This particular reaction is endothermic, which means that heat is absorbed. The
absorption of heat causes the pack to get cold. A hot pack works in the same way, except
it uses a chemical that reacts with water exothermically, which means that heat is given
off. Calcium chloride and magnesium sulfate are typical choices for this chemical. Both
hot packs and cold packs will last for about twenty minutes on average.
Copyright © 2000-2002 Onset Computer Corporation.
LESSON LAYOUT
Student Misconceptions
Misconception
Chemical reactions always generate heat.
Science Concept
Chemical reactions can generate heat or absorb heat.
Rebuild Concept
Use hot and cold pack chemical reactions and let students feel how the
temperature of the substance changes due to the chemical reaction.
Misconception
Heat can be lost, destroyed, or just disappear.
Science Concept
Heat energy is transferred from one object to another or transformed into another
form of energy, but it never just disappears.
Rebuild Concept
With each chemical reaction discuss where the energy comes from and where it
goes. Discuss the kinds of energy that are involved. Make students aware of the
conservation of energy.
Misconception
Color change is always a physical property
Science Concept
Color is a physical property of a substance. Color change, however, is usually the
result of a chemical change.
Rebuild Concept
Describe and/or show chemical formulas of what is occurring when a substance
changes color.
Student Prior Knowledge
TEKS 6.8 (B) analyze energy changes that accompany chemical reactions such as those
occurring in heat packs, cold packs, and glow sticks to classify them as endothermic and
exothermic reactions.
(TEKS 8.9) The students know that substances have chemical and physical properties
should be introduced prior to the study of exothermic and endothermic chemical
reactions.
5 E’s
Engage
Engage 1
Let students squeeze warm-packs and cold-packs from athletic stores. This is a good
kinesthetic activity that allows students to feel heat being generated or absorbed.
Engage 2
Provide each student with a rubber band. Ask students to hold the rubber band to their
upper lips. Does the rubber band feel warm or cool? Ask the students to stretch the rubber
band out and touch it to their upper lips. Does the rubber band feel warmer or cooler than
before?
Engage 3
Provide each lab group with a light stick. Examine stick before and after breaking it.
List as many observations as you can. Group and Label them as physical and chemical
changes/properties.
Explore
Activity: Hot or Not…Adapted from © Project LIFE 1998.
Materials:
Phenol red solution
Sodium bicarbonate powder (baking soda)
Calcium chloride powder
Quart-size freezer bags
Plastic spoons
Goggles
Gloves
Medicine measuring cups
Toothpicks
Procedure
1. Add one spoon full of sodium bicarbonate and 2 spoons full of calcium chloride to a
plastic Ziploc freezer bag.
2. Measure 10 ml phenol red solution in a medicine measuring cup and place the cup
inside the Ziploc freezer bag. Be careful not to spill the phenol red solution. Squeeze
most of the air out of the bag, and then seal the bag.
3. While the bag is still sealed, spill the contents of the phenol red solution inside the
Ziploc freezer bag. Record observations.
4. The Chemical Reaction. The chemical reaction that is occurring is:
CaCl2
Calcium
Chloride
+
→
2NaHCO3
Sodium
Bicarbonate
2NaCl
+
CaCO3
Sodium
Chloride
+
Calcium
Carbonate
H2CO3
Carbonic
Acid
5. The carbonic acid is unstable and breaks down according to the reaction
H2CO3
Carbonic
Acid
→
H2O
Water
+
CO2
Carbon
Dioxide
Questions
1. Name physical properties of a substance such as: its state (solid, liquid, gas), color,
clarity, density, boiling point, solubility, crystal structure, and odor.
2.
Record 3 physical properties for each of the following chemicals.
Substance
Property
Calcium chloride
White, solid brittle,
chalky, has no odor,
large particles
Baking soda
White, powdery, smooth,
has an odor, dry and
won’t clump, tiny
particles
Phenol red solution
Red, liquid, odor, clear,
flows easily
3. Describe what happens when the baking soda and calcium chloride are mixed
together. Nothing happens.
4. Describe what happens when the phenol red solution comes in contact with the
baking soda and calcium chloride. Powders dissolve, turns into a yellow solution,
fizzes, gets hot, the bags gets puffy, and there is a slight sulfur smell.
5. What are evidences of chemical change? Change in color, heat or light produced,
bubbles of gas produced, solid formed in liquid, smell change, texture change.
6. What is an exothermic reaction? An exothermic reaction is one in which energy is
released. In this experiment heat is released.
7. Give 3 examples of everyday exothermic reactions. A burning candle, combustion
when driving a car, compost decay, or cellular respiration.
Explain
Debrief the results of the lab, “Hot or Not.” Allow students to discuss physical change,
chemical reactions, endothermic and exothermic reactions.
Elaborate
Elaboration 1
Activity: Ice Ice Baby
Materials
Sodium bicarbonate
Vinegar
Ziploc freezer bag
Plastic spoon
Medicine measuring cup
Procedure
1. Add one spoon full of sodium bicarbonate to a plastic freezer bag. Record
observations.
1. Measure 10 ml of vinegar in a medicine measuring cup and place the cup inside the
Ziploc freezer bag. Be careful not to spill the vinegar. Squeeze most of the air out of
the bag, and then seal the bag.
2. While the bag is still sealed, spill the vinegar in the medicine measuring cup inside
the Ziploc freezer bag. Record observations.
Questions
1. What is an endothermic reaction? An endothermic reaction is one in which energy is
absorbed. In this experiment heat is absorbed and the bag becomes cold to touch.
3. Give 3 examples of everyday endothermic reactions. Photosynthesis, photography,
cold packs, setting of plaster of Paris.
The bag will feel cold to touch when sodium bicarbonate is mixed with vinegar. This
chemical reaction is called an endothermic reaction because heat is taken in as it is
absorbed into the reactant (sodium bicarbonate). In this experiment, the temperature of
bag drops.
The students may also design their own experiment to determine which combination of
chemicals produces an endothermic reaction. Provide students with the following
substances: sodium bicarbonate, water, phenol red, and calcium chloride. When sodium
bicarbonate is mixed with a liquid, an endothermic process occurs.
Elaboration #2
Activity: Full of energy
Materials
50 mL beaker
Thermometer
Goggles
Gloves
glass stirring rod
plastic spoon
copper (II) chloride dehydrate
15 cm square of aluminum foil
 Always use caution when working with chemicals. Wear
goggles and check how to discard the resulting solutions.
Procedure
Record observations in the table as your perform the experiment.
1. Place 25 ml of tap water in a beaker. Take the temperature of the water.
4. Add 5 milliliters of copper (II) chloride dehydrate crystals to the beaker. Do NOT stir
the solution. Take the temperature of the solution.
5. Stir the mixture with the glass rod until the crystals dissolve. Take the temperature of
the solution.
6. Crumple the 15 cm square of aluminum foil into a ball and carefully place it in the
solution. DO NOT LOOK DOWN INTO THE BEAKER but rather make
observations from the side of the beaker.
7. Observe the mixture for 10 minutes and record any change in temperature.
8. Pour liquids down the sink with water. Discard solids in a chemical waste container
provided by the teacher. Wash your hands thoroughly.
Procedure
Observations
Examine dry Copper (II) chloride dehydrate
Add 5 ml of Copper (II) chloride dehydrate
crystals to 25 ml of tap water
Stir mixture until crystals dissolve
Carefully place aluminum foil ball into
solution
Monitor temperature for 10 minutes
9. Question: Is this an endothermic or exothermic reaction? Exothermic Why? Heat is
given off.
Elaboration #3
Activity: I scream, you scream, we all scream, “Ice Cream”
Materials
½ cup milk or cream
1 teaspoon vanilla
1 Tablespoon sugar
4 cups crushed ice
4 Tablespoons salt
Thermometer
Quart size freezer bag (2)
Gallon size freezer bag
Use the following materials and procedures to continue investigating endothermic and
exothermic reactions and processes. In this laboratory activity, you will explore energy
changes that occur during the process of making ice cream.
Procedure
1. Mix milk, vanilla, and sugar together in a quart sized Ziploc freezer bag. Remove
air and zip closed.
2. Place the bag in a second quart sized Ziploc freezer bag to provide extra
protection for the ice cream in case the seal accidentally breaks.
3. Place the double-bagged ice cream mixture into a gallon size Ziploc freezer bag.
Fill the gallon baggie ½ full with ice and layer in 6 tablespoons of salt. Remove
extra air from the gallon bag and seal it closed.
4. Use your hands to carefully shake or massage the gallon size Ziploc freezer bag
for about 2 minutes. It is possible to wrap the freezer bag in a towel or use gloves
if the mixture is too cold for the students to handle.
5. Crack open the seal of the gallon bag, slide the thermometer in and take the
temperature of the outside of the ice cream baggie. Record the temperature in
the table. Remove the thermometer and reseal the gallon bag.
6. Continue shaking and massaging the gallon size Ziploc freezer bag. Repeat step
#5 every two minutes for approximately 15 minutes.
Minutes
Temperature of the
OUTSIDE of ice
cream baggie
0
2
4
6
8
Complete the following questions or activities.
1. Based on you observations, Is the ice cream mixture an endothermic or
exothermic process? What about the salt & ice mixture? Exothermic for ice
cream, endothermic for salt-ice-water.
2. Create a graph of the results.
3. Explain how heat is gained or lost in this experiment. Heat is transferred OUT of
the ice cream (exothermic) so the left over ice cream gets colder as it heats up the
surroundings. The ice-salt-water mixture is gaining heat from the ice cream,
causing the ice to melt and ice cream to cool off and freeze. Since the salt-icewater mixture is causing the heat to decrease in the surroundings, it is
endothermic.
Evaluation
Use the following table to (1) classify the following as examples of exothermic or
endothermic reactions and (2) identify physical and chemical changes.
TYPE CHANGE?
DESCRIPTION
Physical/Chemical
ENDOTHERMIC OR
EXOTHERMIC?
Physical
Melt ice cubes
Endothermic
Chemical
Rusting iron
Exothermic
Physical
Condensation of rain
Exothermic
Physical
Evaporation of water
Endothermic
Chemical
Combining H2 and O
Endothermic
Physical
Freeze ice cubes
Exothermic
Chemical
Candle flame
Exothermic
Chemical
Cold packs
Endothermic
Chemical
Combustion
Exothermic
Chemical
Setting of plaster of Paris
Exothermic
Chemical
Photosynthesis
Endothermic
Varying amounts of Compounds A and B were added to separate containers and then
dissolved in 500 ml of water. As each quantity of the compound was added to each of the
containers, a temperature was recorded. Use the graph to answering the following
questions.
2. What is the independent (manipulated) variable? Amount of the compound
3. What is the dependent (responding) variable? Temperature of the solution
4. According to the graph, is the chemical reaction for Compound A endothermic or
exothermic? Endothermic
5. According to the graph, is the chemical reaction for Compound B endothermic or
exothermic? Exothermic
6. Predict what would happen if 30 milliliters of Compound A were dissolved in 500 ml
of water. The temperature would remain at 20° Celsius
7. Predict what would happen if 50 milliliters of Compound B were dissolved in 500 ml
of water. The temperature would remain at 45° Celsius
8.
Assuming there is no chemical interaction between Compound A and Compound B,
predict the final temperature of a mixture containing 15 milliliters of Compound A
and 5 milliliters of Compound B. The temperature would be 24° Celsius. One
teaspoon of Compound B does not change the temperature.
9. List at least two variables that should be controlled in this experiment. Answers will
vary.
Effect of Compound Amount on
Temperature of Solution
Temperature
(Celsius)
50
40
41
37
30
30
26
24
20
44
45
45
22
20
20
10
0
0
1
2
3
4
5
Amount of Compound (milliliters)
Compound A
Compound B
6
7
Hot or Not
Materials
Phenol red solution
Sodium bicarbonate powder (baking soda)
Calcium chloride powder
Quart-size freezer bags
Plastic spoons
Medicine measuring cups
Toothpicks
Procedure
1. Add one spoon full of sodium bicarbonate and 2 spoons full of calcium chloride
to a plastic Ziploc freezer bag.
2. Measure 10 ml phenol red solution in a medicine measuring cup and place the cup
inside the Ziploc freezer bag. Be careful not to spill the phenol red solution.
Squeeze most of the air out of the bag, and then seal the bag.
3. While the bag is still sealed, spill the contents of the phenol red solution inside the
Ziploc freezer bag. Record observations. Name physical properties of each
substance such as: its state (solid, liquid, gas), color, clarity, density, boiling
point, solubility, crystal structure, and odor.
Substance
Calcium chloride
Baking soda
Phenol red solution
Final product
Property
Questions
1. Describe what happens when the sodium bicarbonate and calcium carbonate are
mixed together.
2. Describe what happens when the phenol red solution comes in contact with the
sodium bicarbonate and calcium chloride.
3. What are evidences of chemical change?
4. What is an exothermic reaction?
5. Give 3 examples of everyday exothermic reactions.
ICE ICE BABY
Materials
Sodium bicarbonate
Vinegar
Ziploc freezer bag
Plastic spoon
Medicine measuring cup
Procedure
1. Add one spoon full of sodium bicarbonate to a plastic freezer bag. Record
observations in Table 1
2. Measure 10 ml of vinegar in a medicine measuring cup and place the cup inside
the Ziploc freezer bag. Be careful not to spill the vinegar. Squeeze most of the air
out of the bag, and then seal the bag.
3. While the bag is still sealed, spill the vinegar in the medicine measuring cup
inside the Ziploc freezer bag. Record observations.
Questions
10. What is an endothermic reaction?
11. Give 3 examples of everyday endothermic reactions.
FULL OF ENERGY
Procedure
Observations
Materials
50 mL beaker
thermometer
glass stirring rod
plastic spoon
copper (II) chloride dehydrate
15 cm square of aluminum foil
Procedure
1. Record observations in the table as your perform the experiment.
2. Place 25 mL of tap water in a beaker. Take the temperature of the water.
3. Add one teaspoon of copper (II) chloride dehydrate crystals to the beaker. Do
NOT stir the solution. Take the temperature of the solution.
4. Stir the mixture with the glass rod until the crystals dissolve. Take the temperature
of the solution.
5. Crumple the 15 cm square of aluminum foil into a ball and carefully place it in the
solution. DO NOT LOOK DOWN INTO THE BEAKER but rather make
observations from the side of the beaker.
6. Observe the mixture for 10 minutes and record any change in temperature.
7. Pour liquids down the sink with water. Discard solids in a chemical waste
container provided by the teacher. Wash your hands thoroughly.
8. Is the reaction endothermic or exothermic? What evidence do you have?
Examine dry Copper (II) chloride dehydrate
Add 15 ml of Copper (II) chloride dehydrate
crystals to 25 ml of tap water
Stir mixture until crystals dissolve
Carefully place aluminum foil ball into solution
Monitor temperature for 10 minutes
CHILL OUT
Materials
50 ml graduate cylinder
250 ml beaker
Balance scale
Citric acid solution
Baking soda
6 M hydrochloric acid solution (CAUTION)
Goggles
Gloves
Apron
Magnesium ribbon
Thermometer
Glass stirring rod
Styrofoam cup
Be sure to wear goggles at all times and notify your teacher in case of an accident.
CAUTION: Hydrochloric acid is caustic. Do not spill it on your skin or clothing.
Part A
1. Place a Styrofoam cup inside a 250 ml beaker. Measure 30 ml of citric acid
solution and add it to the Styrofoam cup. Place a thermometer into the solution.
Record the temperature in the table.
2. Measure 10.0 g baking soda. Add the baking soda to the citric acid solution and
stir with a glass stirring rod. Record the temperature every 20 seconds for about 5
minutes. Stop recording the temperature when it begins to rise. Use graph paper to
record the results. Connect the data points using a blue map pencil.
3. Flush solution down the sink with water. Rinse the thermometer and dispose of
the cup as directed by the teacher.
Questions:
1. How can you tell that a chemical reaction is taking place?
2. Is the reaction endothermic or exothermic? Why?
Part B
1. Place a Styrofoam cup inside a 250 ml beaker. Measure 30 ml of hydrochloric
acid and add it to the Styrofoam cup. Place a thermometer into the solution.
Record the temperature in the table.
2. Obtain a piece of magnesium metal (approximately 0.1 g). Gently place the
magnesium metal into the cup of hydrochloric acid. CAUTION: Do not
breathe the vapors! Record the temperature every 20 seconds until the
temperature begins to drop. Use graph paper to record the results. Connect the
data points using a red map pencil.
3. Flush solution down the sink with water. Rinse the thermometer and dispose of
the cup as directed by the teacher.
Questions:
1. How can you tell that a chemical reaction is taking place?
2. Is the reaction endothermic or exothermic? Why?
3. Which reaction took place at a greatest rate? Explain your answer using the graph
I scream. You scream. We All Scream for Ice Cream!
Objectives: The student will identify physical changes associated with endothermic and
exothermic reactions.
Objective: The student will demonstrate the loss of heat (exothermic) by recording
temperature data.
Materials
½ cup milk or cream
1 teaspoon vanilla
1 Tablespoon sugar
4 cups crushed ice
6 Tablespoons salt
Thermometer
Quart size freezer bag (2)
Gallon size freezer bag
Use the following materials and procedures to continue investigating endothermic and
exothermic reactions and processes. In this laboratory activity, you will explore energy
changes that occur during the process of making ice cream.
Procedure
1. Mix milk, vanilla, and sugar together in a quart sized Ziploc freezer bag. Remove
air and zip closed.
2. Place the bag in a second quart sized Ziploc freezer bag to provide extra
protection for the ice cream in case the seal accidentally breaks.
3. Place the double-bagged ice cream mixture into a gallon size Ziploc freezer bag.
Fill the gallon baggie ½ full with ice and layer in 6 tablespoons of salt. Remove
extra air from the gallon bag and seal it closed.
4. Use your hands to carefully shake or massage the gallon size Ziploc freezer bag
for about 2 minutes. It is possible to wrap the freezer bag in a towel or use gloves
if the mixture is too cold for the students to handle.
5. Crack open the seal of the gallon bag, slide the thermometer in and take the
temperature of the outside of the ice cream baggie. Record the temperature in
the table. Remove the thermometer and reseal the gallon bag.
6. Continue shaking and massaging the gallon size Ziploc freezer bag. Repeat step
#5 every two minutes for approximately 15 minutes.
Minutes Temperature
of the
OUTSIDE of
ice cream
baggie
0
2
4
6
8
Complete the following questions or activities.
1. Based on you observations, is the ice cream mixture an endothermic or
exothermic process? What about the salt & ice mixture?
2. Create a graph of the results.
3. Explain how heat is gained or lost in this experiment.